Balanced ball mill system with rotary and vibratory movements of the ball mill units



Value Ff 1954 E. w. SMITH 2,693

BALANCED BALL um. SYSTEM WITH ROTARY AND VIBRA-IORY MOVEMENTS OF THE BALL HILL UNITS Filed Feb- 21, 1949 2 Sheets-Sheet l w-W' r-Nodal Point of Qmng l l llll II II II II IIII ll lllllll :INVENI'OR. Eduard M Kori/4 E. W. SMITH Nov. 2, 1954 BALANCED BALL MILL SY 2,693,320 STEM WITH ROTARY mo VIBRATORY MOVEMENTS OF THE BALL MILL uun's Fild Feb. 21. 1949 2 Sheets-Sheet 2 W u mm W 1 W M 5 C C W Q Q vv Y 3 B m mzm @9 5 Lg Q L 3 V m L Q L .1 1 8 L N w im g m LIIL L. w m m m e S r United States Patent i BALANCED BALL MILL SYSTEM WITH ROTARY AND VIBRATORY MOVEMENTS OF THE BALL MILL UNITS Edward W. Smith, Melrose, Mass., assignor to Vibro Dynamic Engineering, Inc., Boston, Mass., a corporation of Massachusetts Application February 21, 1949, Serial No. 77,540

12 Claims. (Cl. 241-175 The present invention relates to ball mills in which material is finely divided in a rotating drum partially filled with metallic balls preferably polished steel balls, and the material to be pulverized. Such ball mills are used extensively in many industrial operations. The process of reducing materials to finely divided desired particle sizes by the use of ball mill usually consumes considerable time and therefore limits production and increases the cost of the ultimate product.

In ball mills of the usual type, the drum containing -the balls and the material which is being worked is usually rotated at some desired constant velocity. This accomplished either by applying balanced forces to substantially equal masses with equal amplitudes or supplying unequal forces to unequal masses with resultant unequal amplitudes. For the most part it is preferable to apply equal forces to substantially equal weights or masses to obtain equal motional amplitudes.

which forms a feature of the present invention, or if theresonant system is not used, a balanced system may still be employed. In the use of a resonant or nonresonant system, the vibrational energy should be applied between the masses. In the case of a resonant system, the resonanceshould also be applied between the masses. The use of a self-resonant system permits operation at resonance irrespective of loading. A further feature of the resonant system of the present inventionis that the amplitude of vibration may be automatically maintained at some pre-set value. In accordance with the present invention, means may also be employed for automatically preventing the system from being operated at all if the rotating drums or jars are too unequally loaded.

The merits and advantages of the present invention will be more fully understood from a consideration of the specification set forth below when taken in connection with the drawings forming a part thereof, in which:

Figure 1 shows schematically a resonant system wlillilch may be used in connection with a vibrating ball m Figure .2 shows diagrammatically the vibration of a resonant system of equal and unequal weights.

Figure 2a shows two curves applicable to the arrangement described in connection with Figure 2.

Figure 3 shows a. self-resonant vibrating ball mill constructed in accordance with the diagram of Figure 1.

This may be accomplished with the use of a resonant system Figure 4 shows a sectional detail of an element indicated in Figure 3. v I Figure 5 shows a further modification of the device shown in Figure 3..

Figure 6 shows a detail taken on the section line 6-6 of Figure 5. I Figures 6a and 6b show detailed wiring diagrams relating to the elements of Figure 5 and Figure 6.

Figure 7 shows a detail taken on the section line 7-7 of Figure 5. p

In Figure 1, attached hereto, I have s hown in schewould not release the masses.

2,693,320 Patented Nov. 2, 1954 matic form, an arrangement which will accomplish the above objectives. of the jars or drums, with their loads of material and balls. S, represents the spring connecting the two together to form a resonant system. It will be noted that the two masses W and W are equipped with arms A, B, and C, A and B being afiixed to mass W, and C to mass W.

The masses W and W, representing the jars with the materials inside, normally will be rotated as will be described later in the specification and will also be vibrated by forces applied between the masses W and W acting to compress the spring S. schematically, this force is applied by the magnet coil M which is energized by a direct current or an alternating current source A through the circuit forming a part of the figure. This circuit comprises a pair of normally closed contacts N1 and N2, a normally open contact Na and a momentary contact starting switch N4. In the operation of the system of Figure 1,'upon the closing of the contacts N4, the circuit through the magnet coil M is completed as follows; from the power source A, the magnet coil M, the starting switch N4, the relay coil N5, either one or both of the contacts N1 and N2, back to the supply source A. When this circuit is momentarily closed, the switch N3 is energized, maintaining current through the magnet coil N5 and acting as a holding relay for the supply of power to the magnet coil M. The masses W and W will be drawn together against the tension of the spring until the arms B and C open both contacts N1 and N2, thus interrupting the energization of the magnet M. The starting switch N4 should be opened substantially the same time that the last switch N1 or N2 is opened. When this occurs, the spring S will take over forcing the masses W and W apart until the arm A strikes against the switch N3, again closing the circuit to the magnet coil M for the repetition of the operation. The coil N5 will of course again act as a holding coil to keep the magnet energized. It is obvious that the system will operate at a resonance depending upon the magnitude of the masses and the restoring forces of the spring. If the jars are equally loaded, the arms B and C will open the contacts N1 and N2 simultaneously. If, however, the jars should be unequally loaded so that the masses W and W are not of substantially the same magnitude, then the amplitude of the heavier mass would be less, and therefore any one of the contacts N1 and N2 will be opened, in which case the system would cease to operate as the coil M would remain energized and The length of the arms B and C may of course be adjusted so that the loading of the jars may be controlled within desirable limits. In fact, if it is desired to operate with the masses unequal in magnitude, this may also be accomplished by contrglling the position or the length of the arms B and It will be evident from the description above that the vibration energy is applied between the two masses, thereby eliminating anyreaction on the foundation supporting the two masses which would otherwise be present if the vibrational energy was supplied to only one of them as has hithertofore been the practice. It will also be noted that the system in accordance with Figure 1 will also operate at the resonant frequency. This is true because the periodic opening and closing of the circuit to the electromagnet can only be done in conformity with the period of the masses which as has been stated is fixed by their relationship to the stiffness ofthe spring. Therefore, the system will always operate at the resonant frequency no matter what may be the loading of the jars which make up the masses. The manner in which the use of the above system makes it impossible for the arrangement to operate if the jars are too unequally loaded will become more apparent from a study of Figure 2. It will also make clear the reason for the use of two sets of normally closed contacts in parallel in the circuit where offhand it would appear that only one is actually needed.

Suppose we have the two masses W and W which are of equal weight and are connected together by spring S. Since the two are of equal weight, oscilla- W and W represent the two masses tion of the system at resonance requires that the two masses move at equal velocities and that their momentums be equal. Under such circumstances to nodal point, that is, the point of zero motion of the spring will be at the center of the spring as shown. For the sake of simplicity let us assume that the spring is dimensionless so that the full amplitude of either weight can be represented by the distance between it and the nodal point. Under the above conditions the two weights will oscillate about their positions at rest, first coming together till they meet at the node and then extending the spring by an equal amount in the opposite direction.

Now let us assume that the two masses are not equal and that W is three times the weight of W. Since it is a characteristic of such an oscillatory system that the momenta of the two sides of the system must be equal, the mass W must move at three times the amplitude of W. Therefore the node under these conditions will no longer be at the center of the spring but will move toward the heavier weight. If the initial starting points under the above conditions are the same as those in the case where the weights are equal, then it will be apparent that the weight W, since it is moving farther from the same starting point, will have to move beyond the position which it would have moved if it had had the same mass as W, and similarly W will have to move less. In other Words the meeting point has shifted to the right.

Going back now to the original discussion covering the operation of the electrical excitation system, suppose we locate the two sets of normally closed contacts at the point Where the node would occur if the two masses were of equal weight. Under these conditions the two contacts would be opened simultaneously and the system would be oscillated normally. Let us now as sume that due to some fortuitous circumstance that the charges of balls and material in the two jars are not equal. Under these conditions when the momentary contact starting switch is closed the electromagnet is energized and the spring will be compressed. If the loads were equal, both of the normally closed contacts referred to above would be opened thereby interrupting the current to the electromagnet with the result that the spring would then expand. Since, however we have assumed that they have been unequally loaded, one only of the pair will open which is not sufficient to interrupt the current and the system will refuse to oscillate until the proper operating conditions are restored.

It is, of course, possible for the operator to load both sides equally but with a much greater load than that for which the system was designed. Under these conditions the system would oscillate but at a lower frequency. It will be apparent from the Figure 2a, however, that a very considerable overload would have to be applied before any appreciable change in frequency took place. Consequently there should be no noticeable change in grinding efficiency due to equal overloading on both sides unless the overloading was so great as to be immediately obvious.

In Figure 2, the abscissae indicate the ratios of the masses M1 to M2 while the ordinates indicate the ratio of the frequencies where F is the frequency for which the mill was designed and Fx the operating frequency with unequal loading. In this case, the curve I was run for a constant magnitude of M1 plus M2, while the curve II was run for a varying magnitude of the sum M1 plus M2. From the curve I, it will be noted that the resonance will be substantially the same for a variation of the ratio Mi/Mz from approximately .6 to 1.4 which is quite nearly to a condition where one weight will be half the other weight or one and onehalf times the other weight. In the case where the system is overloaded, the frequency will drop slowly, while if it is underloaded, the resonant frequency Wlll. rise fairly rapidly.

The method by which the principles of operation discussed above may be applied to an actual ball mill may best be understood by reference to Figure 3 where 1, 1 are the ball mill cylinders themselves, and 2, 2' are the bearings supporting the mill cylinders. The arrangement shown involving two mill cylinders recommended because it is desirable that the mass of one cylinder with its contents be balanced by an equal weight which for economy can well be a second cyllnder although, obviously, equally satisfactory results insofar as the vibration of the system is concerned may be obtained by the use of a compensating mass.

As will be noted, provision is made for the rotation of the two cylinders by gears 4 and 4 which are meshed with smaller gears 5 and 5' carried on shaft 6 which in turn is rotated by motor 7 or some similarly suitable source of power. The rotation of motor 7 therefore serves to bring about a rotation of cylinders 1 and 1. The two cylinders 1 and 1 are mounted in journal bearings 22 and 22' so that they may be free to move axially as well as rotate. Although journal bearings are shown it will be understood that anti-friction ball bearings may also be used provided that they are so arranged as to permit the cylinders to move axially as well as rotationally.

The stiffness required to make the system oscillatory is disposed most conveniently between the two cylinders and comprises a seat 8 secured to the inner trunnion of cylinder 1 and a second seat 8' secured to the inner trunnion of cylinder 1'. 8 and 8 which do not rotate with the cylinders 1 and 1 provide two parallel plane surfaces to which each end of springs 9 and 9 are secured by means of the plugs 19 screwed into the ends of springs 9 and 9' and the cap screws 11 which in turn secure the plugs to the seats 8 and 8'.

It will be seen that the two cylinders with their contents plus the spring system constitute a mechanically resonant system of the two mass type and in conformity with the normal vibration of such a system the two cylinders will tend to fly apanfi'hnd come together at a frequency which is determine j-jby the masses of the cylinders plus their contents, arid thestiffness of the spring system.

Axially mounted between the two seats 8 and 3 is the electromagnetic driving system consisting of field element 12 and the armature element 13. The field element 12 consists conveniently of an E-shaped lamination block having chamfered faces 14 to permit of substantial motion of the armature block 13, to and fro, without substantial change in the perpendicular distance between the field and armature faces. iWhile the angle used is a matter of design for the conditions encountered in a particular machine, an angle of 10 degrees from the horizontal is usually satisfactory.

Excitation of the magnetic circuit composed of the armature and field elements 13 and 12 is obtained from coil 15 whose terminals are connected to conductors 16 and 17. Obviously when current of the proper value flows through coil 15 the springs will be compressed and when the current is cut off the springs will expand, thus bringing about sustained oscillation of the cylinders if the current is reapplied periodically and in unison with the natural period of the system as previously explained. The seats 8 and 8 are connected to a suitable thrust bearing with the rotating supporting shafts for the cylinders so that the seats need not rotate with the cylinder shafts.

The mechanism 31 by which the reestablishment of the current in coil 15 is brought about at the extremity of the outward motion of the cylinder can best be understood by an examination of Figure 4 which shows one embodiment of my invention. A solenoid coil 18 corresponding to N5, Figure 1 is so disposed as to pull to the left a plunger 19 when current flows through the coil. In so doing it compresses spring 23 which normally holdscontacts 21 and 22 corresponding to switch N4, Figure 1, apart which are connected in series with coil 18. Therefore when contacts 21 and 22 are physically closed by some suitable means they will remain closed due to the pull of solenoid coil 18 and will open only under the influence of the spring 23, when the current in coil 18 is interrupted. They will likewise remain open until physically closed again.

The physical closure of contacts 21 and 22 is effected by plunger 24 which is likewise held away from contact 22 by means of spring 25. A plate 25 at the outer end of the stem of the plunger 24 is held in contact with the plate 26 secured to the trunnion of the cylinder 1.

By reference to Figure 3, it will be noted that the element illustrated in Figure 4 is mounted, as shown in Figure 3, on the end of the machine frame. Thus when the expansion of the springs 9 and 9' moves the cylinders outward and forces plunger 24 toward the that of Figure 3.

left closing contacts Zljand; 22[which" energizes can 18 keeping them closed. Since the currentjflowing lIT'COll '18 is likewise flowing through-coillsit will be seen that as soon as the extremity of the stroke has been attained coil 15 is automatically reenergizedqto compress sprlngs *9 and 9 to repeat the cycle. 1 v

The same arrangement for-'interrupting'the magnet circuit shown'in Figure 1 may also' be applied to Figure 3. In this case the 'switch -box 26 may be] provided with two pairs of contacts eachhav'ing'projecting pins'27 and 28 which may be actuated by the arms 29 and 30 corresponding tothearms=B-and C inFigure 1.

This will open the circuit to the energizing coil 15 and porting structureupon which it is mounted,'and' the driving motors 33. .The ball mill 32 may be supported for rotation by suitable bearing supports 34 and 35-wh1ch together with the, motor 33 are all mounted ona-plate or platform 36. The'platform 36 together Wlth the mechanism mounted onxit is free'to move in a longitudinaldirection on thebase 37. The platform 36 on the underside may have grooves 38 and 39 in which a km of ball bearings 40 may be arranged to provideas far ,as possible'frictionless motion ofthe platform 36-.on.the

base 37. The inner bearing: support-34 may. be built up as a plate to the inner side of which the vibrated mechanism for the 'system'may be attached. This arrangement may be similarto that described in co nnection with Figure 3. The springs 41, of which'three are shown but morejor less may be used, are held to the plates 34 by means of. theplugs 42 which are secured. to the "plates 34.

Between the'two plates 34 is mounted the energizingicoil 43 which may beheld in place by a support 44 extending from the base .37. The energizing-coil 43 may: be of a solenoid type with plungers 45'. projecting from the inside of the plates 34 into the center hole of the solenoid.

The control mechanism for opening and closing the circuits may bemounted onthe b'ase 37. The switch box 45" contains theswitch contacts correspondingitotNr .and N2 of Figure 1, and the projectingbars 46 and'47 corresponding to the bars B and C of Figure 1. The switch box 48 which may in this case contain switch contacts corresponding to Na, and holding coils correspondingto N5 are operated by the right angle bars 49 and 50 which correspond to the bar A of Figure 1. The outward move ment of the bars 49 and 50 will close two switches in series. corresponding to the switches N3 and thereby establish the inward movement of the drums. The advantage of this construction is that within the desired lnmts the outward amplitude of the vibration of the drum will be controlled and this will insure equal outward amplitudes for the drums or jars. The advantage of the system shown in Figures 5, 6, and 7 is that relative motion of the drums or jars 32 with respect to the bearing supports will be avoided and it is also possible to connect the drums or jars directly to the driving shaft motor since the armature or the rotating element of the electric motor similarly as in the structure of the other figures w1ll not have to move longitudinally on its axls.

In the system shown in these figures, the resonance will be a balanced resonance and therefore no extraneous vibrations will be produced.

Having now described my invention I clam:

1. Ball mill apparatus of the type described comprlsmg a ball mill jar, said ball mill jar having substantially an axis of symmetry, means mounting said ball mill ar both for rotation about said axis of symmetry and for linear oscillation along said axis, means for rotating the same, a body having an axis of symmetry, said body having a mass ratio to that of the ball mill and load between 9.6 and 1.4 adapted to be carried thereby, means mount1ng said body for oscillatory movement with its axis of symmetry in substantial axial alignment with the rotational axis of said ball mill jar, and means positioned between said ball mill jar and said body for oscillating said body and said ball mill jar simultaneously in opposing directions along said rotational axis, sald last means havmg driving electro-magnetic elements act1ng 1n linear parallel alignment with said rotational axis and connected on the one side of said last named means to said ball mill and on the other side' of said last named means to said body.

2. Ball mill apparatus of the type described comprising a pair of ball mill jars, means mounting each of said jars for rotation including shafts and bearings therefor means for independentlyrotating each of said ball mill jars, independent platforms mounting each of said ball mill jars, means supporting said platforms for free longitudinal oscillation in the direction of said shafts and means comprising electromagnetic and spring means for oscillating said platforms at resonance. v

3. Ball mill apparatus of the type described, comprising a pair of ball-mill jars, means mounting said jars' in spaced axial alignment for free linear axial movement and for axial rotation, means for rotating said ball mills, means acting between said ball mills for oscillating'the same along the'axis of alignment simultaneously towards and then awayfrom each other, said means including electro-magnetic means providing forces acting wholly parallel to the axis of alignment and spring means energized when the motion of the jars are towards each other for providing the forces also acting parallel to said axis of alignment for moving the jars away from each other.

4. Ball mill apparatus of the type described comprising a pair of ball mill jars, means mounting said jars in spaced axial alignment for free linear axial movement and for axial rotation, means for rotating said ball mills, means acting between said ball mills for oscillating the same along the axis of alignment simultaneously towards and then away from each other, said means comprising electro-magnetic means providing forces acting wholly parallel to said axis of alignment for drawing said jars together and spring means energized thereby, said spring means also providing forces acting wholly parallel to said axis of alignment and control means operated. at "the extremities of movement of said jars for controlling the operation of said drawing means.

5. Ball mill apparatus of the type described comprising a pair, of ball mill jars, means mounting said jars in spaced axial alignment for free linear axial movement and for axial rotation, means for rotating said ball mills, means acting between saidball-mills for osc1llating the same along the axis of alignment simultaneously towards and then away from each other, said means comprising electromagnetic means providing forces act1ng Wholly parallel to said axis of alignment operative to draw said jars together a given amplitude, spring means adapted to be energized by the actuation of said electromagnetic means for forcing said jars apart and electrically operated control means for deenergizing and energizing said electromagnetic means at the extremities of the motion of said jars.

6. Ball mill apparatus of the type described comprising a pair of ball mill jars, means mounting each of said ars for rotation including shafts and bearings therefor means for'independently rotating each of said ball mill jars, independent platforms mounting each of sa1d ball mill ars, means supporting said platforms for free longitudinal oscillation in the direction of said shafts and means comprising electromagnetic and spring means for oscillating said platforms at resonance including control means having limit switches for energizing and deenerglzmg said electromagnetic means.

7. Ball mill apparatus of the type described comprising a pa1r of ball milljars, means mounting said jars in spaced axial alignment for free linear axial movement and for rotation, means for rotating said ball mills, means mcluding elastic stiffness means and electromagnetic means acting between the ball mill jars provldmg forces acting wholly parallel to said axis alignment for oscillating the latter at resonance and control meansoperatively associated with the amplitude of said ball mill ars for deenergizing said electromagnetic means for stopping the oscillation of said ball mill jars when they are substantially unequally loaded.

8 Ball m ll apparatus of the type described comprising a pair of ball mill jars, means mounting said ars 1n spaced axial alignment for free linear axial move ment and for axial rotation, means for rotating said ball mills, means including elastic stiffness means and electromagnetic means acting between the ball mill jars providing forces acting wholly parallel to said axis of alignment for oscillating the latter at resonance and control means operatively associated with the amplitude of said ball mill jars for deenergizing said electromagnetic means for stopping the oscillation of said ball mill jars when they are substantially unequally loaded,

said last means including two limit switches normally closed, connected in parallel with each other, and in series with said electromagnetic means and means positioning said switches for deenergizing said electromagnetic means when the desired amplitude of each of said ball mill jars is attained.

9. Ball mill apparatus of the type described, comprising a pair of ball mill jars, means mounting said jars in spaced axial alignment for free linear axial movement and for axial rotation, means for rotating said ball mills, means including elastic stiffness means and electromagnetic means acting between the ball mill jars providing forces acting wholly parallel to said axis of alignment for oscillating the latter at resonance and control means operatively associated with the amplitude of said ball mill jars for deenergizing said electromagnetic means for controlling the oscillation of the ball mill jars consisting of two limit switches normally closed, connected in parallel with each other and in series with said electromagnetic means, means positioning said switches for deenergizing said electromagnetic means when desired amplitude of each of said ball mill jars towards one another is attained and switch means po- 1, a

sitioned to be closed by the motion of said jars away from one another for closing the electromagnetic circuit when one of said jars has reached its desired amplitude of motion in the reverse direction.

10. Ball mill apparatus of the type described, comprising a pair of ball mill jars, means mounting each of said jars for rotation, aligned shafts securely supporting said jars having free axial movement and bearings therefor, thrust coupling means secured at one end of each jar shaft, means attached, part to each of said thrust couplings forming an electromagnet and armature for drawing said shafts longitudinally towards one another, spring means, and means positioning said spring means to be compressed by the drawing of said electromagnet and armature together for forcing said shafts longitudinally apart from one another, and a control means for energizing and deenergizing said electromagnet timed with the operation of said electromagnet and said spring means whereby said jars are oscillated longitudinally on said bearings.

11. Ball mill apparatus of the type described comprising a pair of ball mill jars, means mounting each ,f.8 of said jars for rotation including aligned shafts securely supporting said jars having .free axial movement and bearings therefor, thrust coupling means secured at one end of each jar shaft, means attached, part to each of said thrust couplings, forming an electromagnet and armature for drawing said shafts longitudinally towards one another, spring means, means positioning said spring means to be compressed by the drawing of said electromagnet and armature together for forcing said shafts longitudinally apart from one another and switch means for controlling the operation of said electromagnetic .means including means operating said switch means for deenergizing thewsard electromagnet when the spring is energized, and means operating said switch means for energizing .saidelectromagnetic means when the spring is deenergized.

12. Ball mill apparatus of the type described com prising a pair of ,ball mill jars, means mounting :each of said jars for rotation including aligned shafts securely supporting said ljars having free axial movement and bearings therefor, 'a motor having a pinion shaft, gears attached to said jars engaging said pinion shaft whereby said jars are rotated, thrust coupling means secured at one end of each jar shaft, means attached, part to each of said thrust couplings forming an electromagnet and armature for drawing said shafts longi tudinally towards one another, spring means, and means positioning said spring means to be compressed by the drawing of said electromagnet and armature together,

said spring means forcing said shafts longitudinally apart from one another when the electromagnet is inactive.

References Cited in the file of-this patent UNITED STATES PATENTS Number Name Date 195,120 Golding Sept. 11, 1877 2,137,753 Flint Nov. 22, 1938 2,297,486 Linke et al Sept. 29, 1942 2,613,036 Robinson -'Oct. 7, 1952 FOREIGN PATENTS Number Country Date 13,722 Great Britain Dec. 13, 1909 703,862 Germany Mar. 18, 1941 708,694 Germany July 26, 1941 

